diff --git a/src/rendezvous_server.rs b/src/rendezvous_server.rs
index eaf7190f9..e29db1391 100644
--- a/src/rendezvous_server.rs
+++ b/src/rendezvous_server.rs
@@ -16,7 +16,7 @@ use hbb_common::{
         register_pk_response::Result::{TOO_FREQUENT, UUID_MISMATCH},
         *,
     },
-    tcp::FramedStream,
+    tcp::{Encrypt, FramedStream},
     timeout,
     tokio::{
         self,
@@ -31,7 +31,7 @@ use hbb_common::{
     AddrMangle, ResultType,
 };
 use ipnetwork::Ipv4Network;
-use sodiumoxide::crypto::sign;
+use sodiumoxide::crypto::{box_, sign};
 use std::{
     collections::HashMap,
     net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr},
@@ -51,7 +51,7 @@ const REG_TIMEOUT: i64 = 30_000;
 type TcpStreamSink = SplitSink<Framed<TcpStream, BytesCodec>, Bytes>;
 type WsSink = SplitSink<tokio_tungstenite::WebSocketStream<TcpStream>, tungstenite::Message>;
 enum Sink {
-    TcpStream(TcpStreamSink),
+    TcpStream(TcpStreamSink, Option<Encrypt>),
     Ws(WsSink),
 }
 type Sender = mpsc::UnboundedSender<Data>;
@@ -852,8 +852,13 @@ impl RendezvousServer {
         if let Some(sink) = sink.as_mut() {
             if let Ok(bytes) = msg.write_to_bytes() {
                 match sink {
-                    Sink::TcpStream(s) => {
-                        allow_err!(s.send(Bytes::from(bytes)).await);
+                    Sink::TcpStream(s, encrypt) => {
+                        let bytes = if let Some(encrypt) = encrypt.as_mut() {
+                            Bytes::from(encrypt.enc(&bytes))
+                        } else {
+                            Bytes::from(bytes)
+                        };
+                        allow_err!(s.send(bytes).await);
                     }
                     Sink::Ws(ws) => {
                         allow_err!(ws.send(tungstenite::Message::Binary(bytes)).await);
@@ -1215,9 +1220,47 @@ impl RendezvousServer {
                 }
             }
         } else {
-            let (a, mut b) = Framed::new(stream, BytesCodec::new()).split();
-            sink = Some(Sink::TcpStream(a));
-            while let Ok(Some(Ok(bytes))) = timeout(30_000, b.next()).await {
+            let (mut a, mut b) = Framed::new(stream, BytesCodec::new()).split();
+
+            // Recent logged-in clients secure the TCP rendezvous channel before
+            // sending requests. Advertise an ephemeral box key signed by the
+            // server identity so those clients can authenticate this server.
+            // Logged-out and older clients continue below in plaintext.
+            let mut handshake_secret = if let Some(server_sk) = self.inner.sk.as_ref() {
+                let (public_key, secret_key) = box_::gen_keypair();
+                let mut key_exchange = RendezvousMessage::new();
+                key_exchange.set_key_exchange(KeyExchange {
+                    keys: vec![Bytes::from(sign::sign(&public_key.0, server_sk))],
+                    ..Default::default()
+                });
+                a.send(Bytes::from(key_exchange.write_to_bytes()?)).await?;
+                Some(secret_key)
+            } else {
+                None
+            };
+
+            sink = Some(Sink::TcpStream(a, None));
+            let mut receive_encrypt: Option<Encrypt> = None;
+            while let Ok(Some(Ok(mut bytes))) = timeout(30_000, b.next()).await {
+                if let Some(secret_key) = handshake_secret.take() {
+                    if let Ok(msg) = RendezvousMessage::parse_from_bytes(&bytes) {
+                        if let Some(rendezvous_message::Union::KeyExchange(exchange)) = msg.union {
+                            if exchange.keys.len() != 2 {
+                                bail!("Invalid secure TCP key exchange");
+                            }
+                            let key =
+                                Encrypt::decode(&exchange.keys[1], &exchange.keys[0], &secret_key)?;
+                            receive_encrypt = Some(Encrypt::new(key.clone()));
+                            if let Some(Sink::TcpStream(_, send_encrypt)) = sink.as_mut() {
+                                *send_encrypt = Some(Encrypt::new(key));
+                            }
+                            continue;
+                        }
+                    }
+                }
+                if let Some(encrypt) = receive_encrypt.as_mut() {
+                    encrypt.dec(&mut bytes)?;
+                }
                 if !self.handle_tcp(&bytes, &mut sink, addr, key, ws).await {
                     break;
                 }